BOTTOM SHEAR STRESSES IN THE BOUNDARY LAYERS UNDER WAVES AND CURRENTS CROSSING AT RIGHT ANGLES

Richard R. Simons, Tony J. Grass, Mehrdad Mansour-Tehrani

Abstract

This paper describes a two year experimental research programme investigating the influence of non-linear wavecurrent interactions on wave and current characteristics. The tests focus on the mean and oscillatory velocity components and shear stresses within the bottom boundary layer over a rough bed for cases where waves propagate at right angles to the line of the current flow. Bed shear stresses have been measured directly by means of a novel shear plate device. The aim of the research is to generate a reliable data set for use by modellers. Results show that currents experience a significant change both in mean bed shear stress and apparent bed roughness when waves are superimposed. However, the oscillatory, wave-induced, bottom shear stress has been shown to be insensitive to the addition of an orthogonal current.